Pressure actuated switch



Jan. 28,v 1958 P.'B`. SAGAR PRESSURE ACTUATED SWITCH Filed Feb. 20, 1956INVENTOR. PAUL B. SAGAR BYr A T'ORNEK? United S'tates Patent() Thisinvention relates to a pressure actuated switch and Imore particularlyto a simple and inexpensive switch which is capable of being actuated byslight pressure diterentials and which can be accurately adjusted so asto be actuated by a predetermined pressure differential. The switch ofthe present invention has particular utility in air conditioning andheating systems for sounding an 1 alarm when air filters become cloggedbut also has utility u in any environment where it is desired to soundan alarm or actuate a control when a predeterminedpressurediierentialhas been reached between two different gas or air lledspaces.

Pressure yactuated switches of the prior art which are sucientlysensitive to be actuated by very small pressure l differentials, haveeither included diaphragms of large area connected to switch elementsthrough complicated linkages or have included pivoted vanes or plates oflarge size with the switch element carried by a projecting pivot shaftor connected thereto by a linkage mechanism. Such switches have requireddiaphragms or vanes of relatively large size since relatively largeactuating forces were necessary to overcome friction and to insureproper functioning of the switch.

In accordance with the present invention, a mercury switch element ismounted directly on a plate member or vane positioned in the passagebetween spaces containing 1 gas or air at different pressures, the platemember substantially closing the passage when in normal position andbeing pivoted about an axis extending transversely of the passage andeccentric to the pressure areas of the plate member. A simple pivotstructure may be employed imposing substantially no friction forcesresisting movement of the plate member by such diierential pressure. Abiasing force may be provided by a suitable mechanism, such as a weightor a spring, for holding the plate member in a normal position but apreferred structure includes a permanent magnet adjacent the platemember. By adjusting the distance between such magnet and the platemember when the plate member is in its normal position, a simplestructure is provided having a rapid action when the forces due to thepressure differential exceed the magnetic force on the plate member.

` The value of the pressure differential required to actuate the platemember and thus tip the mercury switch to open or close, a circuit canbe adjusted by varying the distance between the plate member and thepermanent magnet and the pressure ditferential required to hold theplate member in its actuated position is less than that required toinitially actuate the plate member.

It is therefore an object of the invention to provide an improvedpressure actuated switch which is operative by small pressurediierentials and which is simple and `reliable in operation.

Another object of the invention is to provide a pressure actuated switchwhich is simple and inexpensive in construction and which will open orclose an electric circuit to Sound an alarm or initiate the actuation ofa control when subjected to a predetermined pressure dilerential.

A further object ofthe invention s to provide a pressure actuated switchin which a plate member is positioned in a passage in a housing andpivoted about aneccentric axis extending transversely of the housing andcarries a mercury switch element mounted directly upon the plate elementso that pivoting of such element by a predetermined pressure dilerentialcauses actuation of the switch.

A still further object of the invention is to provide a switch mechanismin which a mercury switch element is mounted directly upon a pivotedplate member subjected to a pressure differential and in which the valueof such pressure differential required to tip said plate and actuate theswitches may be adjusted by varying the distance between a permanentmagnet and an edge of the plate member.

Other objects and advantages of the invention will appear in thefollowing description given in connection with the attached drawings ofwhich:

Fig. 1 is a vertical section taken approximately through the center of aswitch in accordance with the present invention and showing the switchstructure mounted in the wall of anv air or gas chamber or conduit.

Fig. 2 is a front elevation of the switch of Fig. 1;

Fig. 3 is a rear elevation of the switch of Fig. l;

Fig. 4 is a view similar to Fig. 1 with the wall of the conduit orchamber omitted and showing a modified form of switch;

Fig. 5 is a fragmentary rear elevation of the lower portion of theswitch of Fig. 4; 4

Fig.v 6 is a view similar to Fig. 4 showing a further modified form ofswitch; and

Fig. 7 is a diagrammatic view showing one type of system in which theswitch of the present invention can chamber or duct but it is apparentthat the housing can extend to the exterior of such chamber or duct. The

' passage 17 through the housing 10 has a plate member 18 positionedtherein so as to extend across and substantially fill such passage. InFig. 1 the plate member 18 is shown as being pivoted adjacent its upperedge. Such plate member has a pair of laterally spaced apertures 20 nearits upper edge which receives hook members 22 formed on the downwardlybent forwardly projecting edges of a support member 24 secured to theupper interior portion of the housing 10 by a screw 26.

The plate member 18 has an aperture 28 therein of suftcient size toreceive the body portion of a mercury switch element 30, such switchelement substantially filling the aperture 28. The switch element isheld in position by a spring clip member 32 having a body portionsuitably secured to the plate member 18 and provided with spring arms 34engaging the switch element 30 and holding it firmly against arearwardly bent portion of the body portion of the spring clip member.The plate member 18 is of magnetic material and a small permanent magnet36 is positioned adjacent the lower edge of the plate member 18, thatis, opposite its pivotal connection to the support member 24. Thepermanent magnet 36 is secured to the housing 10, by a screw 38 whichextends through an aper- 'assises ture in the magnet and also securesinposition Va. bracket 40 receiving an adjusting stop screw 42 whichengages the surface of the plate member 18 to set the normal distan'cebetween the vplate member 18 and the magnet 36.

vIt will be apparent that the plate member V18 is held v.againstmovement in a direction toward vthe magnet 36 bya stop serieu/42 butthat itis fre'e topi'vot away from the magnet 36 until its lower endstrikes another'stop screw 44. Suitable tiexibleel'ectrical conductors46 ex- Y tend from the mercury switch element 30 to terminal members 48lmounted upon a terminalstrip 50 of electrical insulating materialsecured to a bracket SZinturn secured to the interior of the housing bythe screw 54.

The operation of the switch of Figs. 1 to 3"sl1`ould be apparent fromtheabove description.y The plate member l 18`may move from its normalposition, shown in Fig. 1,

about its-"pivotal support on 'thel member 24 to a second position inwhiclrthelowe'r edge of the plate member engages against the stopscrew44. It is held in the normal position, shown in Fig. l, by the force ofgravity'and also by magnetic forces provided by the permanent magnet 36.The amount of the latter forces can be adjusted by rotating the stopscrew 42 to vary the distance between the lower edge of theplate member18 and the magnet 36. A pressure differential, of a predetermined magnitude, on opposite sides ofthe plate member 18 and in a Vdirectionurging the plate member from the normal position shown towardv aposition against the stop 44 will cause such movement of the platemember to tip the mercury switch element 30. The switch 'can becalibrated to operate at pressure differentials over a considerablerange by adjusting the stop screw 42. Tipping of the plate elementcarrying the switch element causes closing of the electric circuitthrough the mercury switch element 30 but it is obvious that suchelement can be l reversed and the terminal strip 48 placed at the otherend the inlet side thereof so that a slight partial vacuum is producedin the chamber by the fan 56,. As the filter 58 becomes progressivelyclogged, the vacuum in the chamber 55 increases, that is, the pressurein the duct or chamber lowers to increase the p1'essure-differentialacross the switch 8. At a predetermined differential pressure determinedby the position of the stop screw 42, the switch operates to sound analarm 60, which may be an electric bell energized from a step downtransformer 62, the bell 60 and switch 8 being in series in thesecondary circuit ofthe transformer. Thepressure differential betweenthe interior and exterior of the chamber 55 will ordinarily bel of theorder of a few inches of water, even when the filter S8 is suflicientlyclogged that it should be changed, so that the force available foractuating the plate member 18 vof the switch' is of the order of a fewounces. The

' switch of the present invention, however,l consistently operates at adefinite pressure differential within the range indicated, whichpressure differential can be preset by adjusting the stop screw 42.

The switch of Figs.'4 and 5 is similar to that of Figs.

l to 3,except that the modified plate member 64 is pivotedA at thebottom edge instead of at its top edge. Thus, the plate member 64 mayhave notches 66 in its lower edge I y'received in notches in forwardlyextending, downwardly bent edge portions of a pivot support member 67secured to'the housing68. A mercury'switch element 30of the jsame' typeyemployed in theV switch of Figs. l to 3 is likewise positioned in anaperture 28 inthe plate member 4and Held imposition b`y"a 'spring'clipunernber 32. The

remainder ofthe structure of the switch of-Figs. 4 and 6 may beidentical to that of the switch of Figs. 1 to 3, except that the stopscrew 44 is omitted. That is to say, the switch of Figs. 4 and 6 mayinclude the permanent magnet 36, bracket 40 and stop screw 42 and mayalso include the terminal strip 50 and bracket 52, the bracket 52serving as a stop for the plate member 64 instead of the stop screw 44of Fig. `l. e

A further modified switchis shown in Fig. '6 which may be the same astheswitch shown in Figs. 4 and 5, except that a bl weight 70, which isadjustably secured on a bar 72 extending substantially at right anglestothe plate member 74, is employed to bias vthe plate member 74 toward itsnormal position instead of a permanent magnet. The operating pressure ofthe switch of Fig. 6 can be adjusted by moving the weight along the bar72 and the switch ofl Fig. 6 is satisfactory for certain purposes,although in general', its operating pressure cannot be soaccuratelypredetermined as the switches of Figs. l to 5, inclusive.

I claim:

l. A pressure actuated switch comprising a housing having apassagetherethrough, a plate having a normal positi'onin which vsaidplateextends across and substantially closes said passage, said platebeingpivoted about an axis extending transversely of said passage andadjacent one edge of said plate, a stop preventing movementof vsaidplate in one direction past said normal position, said plate beingmovable in the other direction about said axis between said normalposition and a `second position, a mercury switch element mounteddirectly on said plate adjacent said axis for closing an electriccircuit when said plat'e'is in one of said positions and opening saidcircuit when said plate is in the other of said positions, said platebeing of magnetic material, a permanentr magnet supportedl in saidhousing adjacent the other edge of said plate and positioned to'urgesaid plate in said one direction against said stop, means to. adjustsaid stop and said magnet relative to each other to vary the distancebetween said magnet and said plate when said plate is in-said normalposition so that said plate is moved from said normal position to saidsecond position when the pressure differential in said other directionbetween opposite sides of said plate reaches a predetermined valuedepending upon said distance.

2. A pressure actuated switch comprising a housing having a passagetherethrough, a plate having-a normal position in which said plateextends across and substantially closes said passage, said plate beingpivoted about an axis extending transversely of said passage and ad- Yjacent one edge. of said plate, a stop preventing movement of said platein one direction past said normal position, said plate being movable inthe other direction about said axis between said normal position and asecond position, said plate having an opening therethroughk adjacentsaid axis, a ,mercury switch element mounted in and` substantiallyfilling said opening, said switch element closing an electric circuitwhen said plate is in 4one of saidfpositions and opening said circuitwhen said plate is in the'other ofsaid positions, saidplate being ofmagnetic material, a permanent magnet supported in'said housingadjacentthe 'one edge of said plate and positioned to lurge said plate in saidlother direction against said stop, said stop being adjustable to varythe distance between said magnet and said plate when said plate is insaidnormal position so that said plate is moved from fsaidnormal'p'osition to said second yposi-- tion when 'the'pressuredifierential in said other direction between opposite sides ofsaid plate reaches a predeteri mined value' dependinguponthe positionofsaid stop.

3. A pressure actuated `switch comprising a housing having apassagetherethrough; a` plate having a normal v`position Vinv which :said plateextends across and substantially closes said passage, said vplate beingpivoted about xanaxisextendingtraiisversely ofsaidpassageand adjacentone edge of said plate, a stop preventing movement of said plate in onedirection past said normal position, said plate being movable intheother :direction about said axis between said normal position and asecond position, said plate having an opening therethrough, a mercuryswitch element mounted in and substantially filling said opening, saidswitch element closing an electric circuit when said plate is in one ofsaid positions and opening said circuit when said p-late is in the otherof said positions, said plate being of magnetic material, a permanentmagnet sup ported in said housing adjacent the other edge of said plateand positioned to urge said plate in, said one direction against saidstop, said stop being adjustable to vary the distance between saidmagnet and said plate when said plate is in said normal position so thatsaid plate is moved from said normal position to said second positionwhen the pressure differential in said other direction between oppositesides of said plate reaches a predetermined value depending upon theposition of said stop.

4. A pressure actuated switch comprising a housing having a passagetherethrough, a plate having a normal position in which said plateextends across and substantially closes said passage, said plate beingpivoted for movement about an axis extending transversely of saidpassage, a stop preventing movement of said plate in one direction pastsaid norm-al position, ,said plate being movable in the other directionabout 4said axis between said normal position and a second position, anaperture extending through said plate, an elongated mercury switch tubemounted in and substantially lling said aperture in said plate, saidtube extending transversely of said plate and projecting lateral-lythereof on both sides so that the mercury therein may occupy alternatepositions beyond the plane of the plate, said switch element closing anelectric circuit when said plate is` in one of said positions andopening said circuit when in the other of said positions, bias meansurging said plate in said one direction against said stop, said axisbeing eccentric of said plate so that said plate is moved from saidnormal position to said second position when the pressure differentialin said other direction between opposite sides of said plate reaches apredetermined value.

References Cited in the tile of this patent UNITED STATES PATENTS1,292,334 Larsen Jan. 21, 1919 1,398,892 Dorsey Nov. 29, 1922 1,653,177Herz Dec. 20, 1927 1,693,309 Mettler Nov. 27, 1928 2,214,092 UhlornSept. 10, 1940 2,470,553 Gudmnndsson May 17, 1949 2,679,731 ZearfossJune 1, 1954

